A compressor is, for instance, used in a turbocharger (exhaust turbocharger) mounted to an automobile or the like. A turbocharger has an exhaust turbine for converting energy of exhaust gas into power, and a compressor is driven by power outputted from the exhaust turbine. The compressor compresses air to be fed to an engine during operation, and thereby thermal efficiency of the engine improves, for instance.
A compressor includes a housing and an impeller disposed inside the housing. The impeller includes a hub and a plurality of blades disposed on an outer peripheral surface of the hub, and the outer peripheral surface has a trumpet shape. The housing has a shroud section forming a fluid flow path with the outer peripheral surface of the hub, and a fluid flows through the fluid flow path while having its speed increased by rotating blades. While the housing is normally made from metal such as cast aluminum and cast steel, resin housings are increasingly used in recent years to reduce the weight and costs, for instance.
However, a resin housing has a greater thermal expansion rate than a metal housing, and thus a gap between the housing and blades widens with a temperature increase of the housing, which may decrease the efficiency of the compressor. Furthermore, a resin housing has a lower strength than a metal housing, and needs to be reinforced by increasing the thickness of the housing or by providing a rib, to prevent fragments of an impeller from scattering outside in case of breakage of the impeller, i.e., to enhance the containment property. Such reinforcement, however, may cancel out the merits of weight reduction and cost reduction achieved by employing a resin housing.
To solve the above problems, the compressor disclosed in Patent Document 1 is provided with a metal shroud disposed between an impeller and a resin housing. The metal shroud has a smaller thermal deformation rate than resin, and thus it is possible to relatively reduce a widening amount of the gap between the metal shroud and the blades accompanying a temperature increase of the metal shroud. Thus, providing a metal shroud makes it possible to ensure a high compressor efficiency. Furthermore, a metal shroud has an excellent strength, which makes it possible to ensure a high containment property.